It's often said by electric-car owners and advocates that once you start driving electric, you never want to go back.More >>

It's often said by electric-car owners and advocates that once you start driving electric, you never want to go back.More >>

By John Voelcker

As predicted, the plug-in hybrid version of the 2016 Cadillac CT6 large luxury sedan was released April 20 at the Shanghai Motor Show, using an adaptation of GM's second-generation Voltec hybrid system.

What wasn't predicted was the startling size of its battery pack: 18.4 kilowatt-hours, identical to that used in the 2016 Chevrolet Volt.

That means Cadillac is fitting a battery that's essentially double the size of any other plug-in hybrid on the market today--and should probably achieve 30 or more miles of electric range with it.

Unlike the Volt, however, the CT6 plug-in hybrid will switch on its engine under higher loads, according to the GM press release.

That engine is a turbocharged 2.0-liter four-cylinder with direct injection, presumably a variation on the same engine in the non-hybrid four-cylinder CT6 announced at the New York Auto Show three weeks ago.

While GM didn't break out the power of the engine or the two electric motors in the Voltec hybrid drive system, it said the combined system produces 335 horsepower (250 kilowatts) and 432 lb-ft of torque.

The battery pack is not the "T-pack" used in the Chevy Volt, which sits in the tunnel between the front seats and under the rear seats. Instead, according to Cadillac, it's located "between the rear seat and the trunk," effectively between the rear wheels.

Like the Volt pack, the CT6 plug-in hybrid battery will use GM's "proven active thermal control system that maintains electric range over the battery system's life," it said.

While the U.S. release notes that range estimates will be provided near to the U.S. launch of the car, the Chinese release cites a range of "greater than 60 km" (more than 37 miles).

That number, however, is likely to fall on the more challenging U.S. EPA test, which is adjusted to reflect the agency's best estimate of average real-world use.

"Cadillac expects the fuel economy of the CT6 PHEV to be more than double that of the car's conventional engine offerings" in the U.S., Cadillac said, "as measured by miles per gallon [MPGe] equivalent."

The Chinese model will be rated at approximately 2.0 liters per 100 km, it said, which translates to 118 miles per gallon.

To its credit, however, Cadillac underscored the different testing cycles: "Standards for measuring vehicle fuel economy differ between China and other global regions."

A range of 30 miles or more would be exceeded only by the 2016 Chevrolet Volt, which will have 50 miles of electric range.

Competing plug-in hybrids from Mercedes-Benz and BMW presently use smaller battery packs that provide less range--and probably require more frequent engine operation as well under higher power demands.

"The CT6 Plug-In Hybrid system is designed to provide all-electric driving for most daily commutes," Cadillac said, "while maximizing fuel efficiency by providing blended power from the engine and battery at higher speeds and higher loads, even when energy is stored in the battery."

Compared to the CT6's 18.4 kWh, the Mercedes S-Class S550 Plug-In Hybrid (which will become the S-Class 550e this fall) has an 8.7-kWh pack paired with a 3.0-liter V6 engine.

BMW similarly uses a 9-kWh pack in the X5 xDrive 40e plug-in hybrid SUV it just launched, and that system too will roll out across multiple models in the company's lineup.

The stats for the plug-in hybrid, in other words, indicate that GM understands--perhaps better than any other auto company--the importance of offering maximum electric-only range in its plug-in hybrids.

Like the current Cadillac ELR range-extended electric coupe, the CT6 Plug-In Hybrid will offer varying degrees of "Regen on Demand" that the driver can engage using paddles behind the steering wheel.

It will also have three driving modes: Normal, Sport, and Hold. The latter conserves batterycharge for later use where all-electric operation is desired.

Charging on 120-Volt household current or via a 240-Volt Level 2 charging station is provided for U.S. models, with Chinese models accepting that country's standard 220-volt charging. No recharge times were provided.

The plug-in hybrid Cadillac CT6 will be the first General Motors plug-in hybrid built outside the U.S. Models sold in China will be assembled at a new plant in Pudong Jinqiao, China, and will qualify for the country's New Energy Vehicle incentives.

The North American market will be supplied from GM's Detroit-Hamtramck assembly plant, which now builds the Chevy Volt, the Cadillac ELR, and the Chevrolet Malibu and Impala.

The Cadillac CT6 with conventional powertrains will go into production in December, meaning that the plug-in hybrid version should arrive at dealers sometime late in the first half of 2016.

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